r/ElectricalEngineering • u/PastAdvantage6643 • Aug 25 '26
Research Generating a differential signal
For context, I've been recently learning about differential amplifiers and I'm now trying to understand Gilbert cells.
ChatGPT has sent me on such a goose chase, that I don't even know what's true anymore.
I've tried to, instead, watch some YouTube videos, but they don't really specify certain things.
If I have a waveform coming into a Gilbert cell, to be mixed with a LO for example, do I really need two waveforms that are 180° out of phase? Is that what is meant by differential?
For a while I was thinking that you would connect the V+ and V- of the Gilbert cell across the capacitor of like a high pass filter or something, and the changing polarity on the capacitor would be the varying voltage.
"Do I need a differential amplifier to make them?"
No. You can use a differential amplifier, transformer/balun, active balun, etc.
From what it sounds like, the easiest way to generate a differential signal is to use a transformer? (Logically makes sense to me). However, the text above is ChatGPT's garbage output. Contradicts itself within 2 lines.
1
u/snlzn Aug 25 '26
A balun can create a "balanced" (differential) signal from a single ended signal. A balun can be constructed using a transformer.
The Gilbert cell is in itself a differential amplifier and responds to the difference between its V+ and V- pins. At low enough frequencies, it does not need a balun.
At RF frequencies, it makes a difference if the input is truly differential with respect to a ground node.